Power conversion circuits connected in parallel often share a common load unequally in the absence of load sharing control. These discrepancies are a result of slight difference in the regulated output voltage of each individual converter causing one of the converters to supply nearly all of the load current.
Load current control feedback arrangements are used to constrain these paralleled power converters to supply substantially equal currents to a load. In one illustrative arrangement (U.S. Pat. No. 4,276,590) current sharing between power converters connected in parallel to a common load is accomplished by detecting a difference in currents between the parallel converters and varying the duty cycle of the power swtiches to maintain load current sharing between the paralleled power converters.
A similar load current control is disclosed in NASA technical report N76-26393/8 which discloses a method and apparatus for automatic load sharing among paralleled converters. A current summing and imbalance detecting circuit generate a difference signal combined with the regulating feedback signal of each converter to achieve load current sharing among the paralleled converters.
In many applications converters are paralleled for reliability, redundancy and continuity of power to the output bus. In these applications, the probability of bus voltage excursions and glitches must be minimized. These enumerated and other similar arrangements however respond to connection and disconnection transients and fault conditions with considerable output bus voltage excursions. A considerable bus voltage excursion could occur if one of the paralleled power converter's output or paralleling circuit is suddenly disconnected or connected or if one of the paralleled converters is turned on or off. Also a considerable bus voltage excursion could occur if the paralleling bus is shorted.